Compressor unloaders



1957 E. H. JENSEN COMPRESSOR UNLOADERS Filed Sept. 29, 1955 United States PatentU COMPRESSOR UNLOADERS Erik H. Jensen, Staunton, Va., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa, a corporation of Pennsylvania Application September 29, 1955, Serial No. 537,432

Claims. (Cl. 230-21) This invention relates to refrigerant compressors, and

relates more particularly to unloaders for such compressors.

For reducing the starting loads on the motors which drive reciprocating piston type refrigerant compressors, it is common practice to unload cylinders of the compressors when the latter are started. It is also common practice to unload one or more cylinders of such a compressor for reducing its capacity when its load is reduced. Usually such unloading is accomplished by holding suction valves open during the pressure strokes of their associated cylinders.

This invention accomplishes the unloading of a cylinder of a compressor by increasing its re-expansion volume. In one embodiment of this invention the cylinder head of a compressor is provided with a cavity connecting through a slot with the upper portion of each cylinder to be unloaded. The cavity has an auxiliary hollow piston therein, open at one end and closed at the other. The edge of the open end of the auxiliary piston, in loading position, is seated in the cylinder wall so as to close off the slot. The auxiliary piston has openings near its closed end connecting with the cavity. When unloading is to be accomplished, the auxiliary piston is moved away from the cylinder wall so as to permit gas from the cylinder to flow through the piston into the cavity during compression strokes of the main piston in the cylinder, and to flow from the cavity into the cylinder during suction strokes of the main piston in the cylinder. Advantages are that there is cylinder cooling at all times; there is little loss in efficiency; and that but a small force is required to operate the unloader since only one edge of the unloader is exposed to pressure differentials.

An object of this invention is to unload a cylinder of a compressor by increasing its re-expansion volume.

This invention will now be described with reference to the annexed drawings, of which:

Fig. 1 is a plan view partially in section of a cylinder head of a refrigerant compressor embodying this invention, the section being taken along the line 11- of Fig. 2;

Fig. 2 is a side elevation, partially in section, of the compressor, and

Fig. 3 is a section along the line 3--3 of Fig. 2.

The compressor illustrated by the drawings is a twocylinder one generally similar, except for the unloading construction, to the compressor disclosed in detail in the E. H. Wolfert Patent No. 2,804,493.

The compressor has a cylinder head with a conventional suction chamber 11 therein above a compressor cylinder 12. Valve plates 13 and 14 with slots 15 for conventional discharge reeds and slots 16 for conventional suction reeds, are supported between the cylinder 12 and the chamber 11. A conventional discharge pressure chamber which is not illustrated would be behind the chamber 11 in Fig. 2.

The cylinder head has a cavity 17 connecting by a slot 18 in the cylinder wall with the compressor cylinder 12. The cylinder wall at the bottom of the slot 18 has an annular groove 19 for receiving the open lower edge of a hollow unloader piston 20. The piston has a closed top to which is connected a plunger 21 of an unloader solenoid 22. The piston has slots 24 near its upper end which open into the cavity 17.

The valve plates 13 and 14 have extensions 23 in which are formed circular holes for receiving the unloader piston 19 and a bearing sleeve 25 therearound. The plate extensions and the sleeve provide a seal around the piston for preventing gas from the slot 18 from flowing around the piston into the cavity.

Normally, when unloading is not required the open end of the piston 20 is seated in the annular groove 19, extending across the slot 18, and preventing the passage of gas between the cavity 17 and the cylinder 12.

In operation, when the cylinder 12 is to be unloaded, the solenoid 22 is energized and retracts its plunger 21 which lifts the piston 20 causing its lower end to move away from the cylinder wall so as to permit discharge gas from the cylinder to enter the open end of the piston and to pass through the openings 24 into the cavity 17 during the compression strokes of the main piston in the cylinder. The gas expands in the cavity, delaying the attainment of maximum pressure on the pressure stroke.

During the suction strokes of the main piston in the cylinder, gas flows from the cavity back into the cylinder delaying the attainment of maximum suction pressure. The capacity of the cylinder is therefore reduced an amount depending upon the size of the cavity.

When the unloading period is ended, the solenoid 21 is deenergized so that its plunger 20 which may be spring loaded, moves the piston 19 downwardly so that its lower edge seats in the groove 18, closing off the slot 17 and preventing gas from flowing between the cylinder and the cavity.

While one embodiment of this invention has been described for the purpose of illustration, it should be understood that the invention is not limited to the exact apparatus and arrangement of apparatus illustrated, since modifications thereof may be suggested by those skilled in the art, without departure from the essence of the invention.

What I claim as my invention is:

1. A compressor having a cylinder in which gas is compressed, a cylinder head for said cylinder, said compressor having a cavity off-set with respect to said cylinder, said compressor having a slot opposite one end of said cavity for connecting said cylinder to said one end of said cavity, a hollow piston in said cavity, said piston normally extending across said slot and having an open end with an edge in contact with the side of said slot opposite said cavity, and having an opening connecting with said cavity, and means for moving said piston from across said slot for permitting gas to flow between said cavity and said cylinder.

2. A compressor as claimed in claim 1 in which the side of the slot where it is normally contacted by said open end of said piston has an annular groove shaped to receive said open piston end.

3. A compressor having a cylinder in which gas is compressed, a cylinder head for said cylinder, said head having a cavity therein off-set with respect to said cylinder, the wall of said cylinder having a slot extending in alignment with said cavity, a hollow piston extending in said cavity and slot, said piston having an open end normally in contact with the side of said slot opposite said cavity, sealing means extending around said piston between said slot and cavity for preventing the passage of gas from said slot into said cavity around said piston, said piston having an opening connecting the interior thereof with said cavity, and means for moving said piston away from said one side of said slot for permitting gas from said cylinder to pass through said slot into said open end of said piston and through said opening into said cavity.

4. A compressor as claimed in claim 3 in which valve plates are supported between the head and cylinder, and in which the sealing means includes said plates.

5. The invention claimed in claim 4 in which the cylinder Wall at said one slot side has a groove therein shaped to receive the open end of the piston.

References Cited in the file of this patent UNITED STATES PATENTS Cummings Oct. 24,

Kurth Jan. 12,

Rochow May 11,

Blache Feb. 27,

Ritter Jan. 3,

FOREIGN PATENTS Germany Aug. 18, 

